In a rotary-press printing on a web, some methods have been proposed which print a pattern of any size or repeat length without the necessity of exchanging plate cylinders, one example is disclosed in Japanese Pat. No. 35-7195, of June 15, 1960.
In this prior art device, the traveling speed of the web or the peripheral speed of the plate cylinder was rapidly varied while printing was not being carried out, that is to say while there was no contact between the web and the plate cylinder. However, there were some problems with this method which had to be solved. Typical problems are as follows:
(a) The web may be easily broken because the web speed is quickly increased or decreased, and this makes registering the printing patterns harder.
(b) If the plate cylinder is rotated in a rapid increment or decrement, it is necessary to use a high powered motor to rotate the plate cylinder, and this also makes it difficult to register the printed patterns.
The present inventors diligently sought to overcome the above problems, and finally found that prints of any repeat length could be made by differentiating between the web speed and the peripheral speed of the plate cylinder, which is an example of printing means. Some patent applications relating to such printing system have been already filed in the Japanese Patent Office, for example published unexamined Japanese application Nos. 62-183348 and 62-227683 of Aug. 1, 1987 and Oct. 11, 1987.
The present inventors continued working on the problems and found that the contact line between the web and the printing cylinder still had little a bit of width, although it was referred to as "line contact," and they found the width of the contact affected the quality of printing, and that the quality could be raised by making the contact line narrower.
In this specification the term "web" is understood to mean something continuous, long and thin, and includes rolled paper, rolled film, linerboard, kraft paper for bags, rolled foil etc. which can be printed on. The material of the web is not limited other than in this respect.